1. Field of the Invention
This invention relates to an actuator control apparatus which controls the operation of an actuator such that a state value, which changes according to operation of the actuator, coincides with a target value.
2. Description of the Related Art
One well-known mechanism which is driven by an actuator is, for example, as shown in FIG. 16, a synchronizing mechanism 110 of a transmission, in which a synchronizer ring 103 is provided between a coupling sleeve 101 which rotates integrally with an input shaft 100 connected to an automobile engine and a synchronized gear 102 provided rotatably but immovably along the shaft on the input shaft 100 connected to a driving wheel (not shown), such that by moving the coupling sleeve 101 by means of the actuator 105 through a shift fork 104, the coupling sleeve 101 and synchronized gear 102 can be switched between connection and disconnection.
In the synchronizing mechanism 110, the coupling sleeve 101 has a hollow construction, and a spline 111 is formed on the inner surface of the hollow portion. Also, a spline 112, capable of engaging with the spline 111 of the coupling sleeve 101, is formed on the outer surface of the synchronizer ring 103, and a spline 113 capable of engaging with the spline 111 of the coupling sleeve 101 is formed on the outer surface of the portion of the synchronized gear 102 opposing the synchronizer ring 103.
When the coupling sleeve 101 and the synchronized gear 102 are connected, the coupling sleeve 101 is moved in the direction of the synchronized gear 102 by the shift fork 104. When the coupling sleeve 101 and synchronizer ring 103 make contact with each other and the synchronizer ring 103 is pressed against the synchronized gear 102, the friction force occurring between the synchronizer ring 103 and the synchronized gear 102 causes the rotation speed of the synchronized gear 102 to be increased or decreased.
As a result, the rate of rotation of the coupling sleeve 101 and the rate of rotation of the synchronized gear 102 are synchronized, the spline 111 of the coupling sleeve 101 is engaged with the spline 112 of the synchronizer ring 103, and moreover the coupling sleeve 101 is moved, and the spline 111 of the coupling sleeve 101 is engaged with the spline 113 of the synchronized gear 102.
Here, if the speed of motion of the coupling sleeve 101 is too fast when the coupling sleeve 101 presses the synchronizer ring 103 against the synchronized gear 102, the coupling sleeve 101 may rebound when the coupling sleeve 101 makes contact with the synchronizer ring 103, or the coupling sleeve 101 may be pressed against the synchronized gear 102 with excessive force, so that the synchronizing mechanism 110 may be damaged.
Hence in the prior art, when the coupling sleeve 101 is moved in the direction of the synchronized gear 102, the speed of motion of the coupling sleeve 101 was reduced when the distance between the two became less than a prescribed value. Also, methods are known in which a spring or other mechanical cushioning mechanism is provided between the actuator 105 and shift fork 104, to reduce the shock at the time of contact of the coupling spring 101 and the synchronizer ring 103 (see for example Japanese Patent Laid-open No. 2002-195406).
From the time the coupling sleeve 101 makes contact with the synchronizer ring 103 until the time engaging of the coupling sleeve 101 and the synchronized gear 102 is completed, it is necessary to press the coupling sleeve 101 against the synchronizer ring 103; but if the pressing force is excessive, damage to the synchronizing mechanism 110 may occur. Consequently the operation of the actuator 105 must be controlled such that the pressing force reliably matches a preset target level.